JP4653528B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device having a fixing roller for fixing a toner image used in an image forming apparatus such as a copying machine, a printer, and a facsimile, and an image forming apparatus including the fixing device.

2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic method, after a toner image formed on a photoreceptor is transferred to a sheet, the sheet is conveyed to a fixing device and fixed by heat and pressure. Examples of the fixing device include a belt fixing method, a heat roller method, and the like (see, for example, Patent Document 1).
In a fixing device incorporating a very high temperature heat source, it is essential to prevent the paper from being wrapped around one of the fixing roller pair (or fixing belt). In the conventional device, the downstream side of the nip portion of the fixing roller pair is required. In general, a separation claw is provided on the outer periphery of the fixing roller so that the leading edge of the conveyed paper is peeled off to prevent winding.
However, if the separation (removability) of the leading edge of the paper is extremely reduced due to breakage of the separation claw, the paper is wound around the fixing roller (or fixing belt), and the image forming apparatus is damaged or jammed. Will significantly reduce the performance.
FIG. 4 is a schematic view showing an example of a fixing device having a detecting means for detecting a winding state other than the separation claw. As shown in FIG. 4, the fixing roller pair constituting the fixing device 1 includes a heating roller 2 incorporating a heater 4 and a pressure roller 3 that forms a fixing nip portion facing the heating roller 2. A separation claw 5 for separating the paper 8 conveyed to the fixing nip portion from the heating roller 2 is disposed.
Further, FIG. 4 shows a remaining paper detection sensor 6, an upper conveyance guide 9 and a lower conveyance guide 10 that form a conveyance path for the paper 8, and a paper conveyance sensor 7 that detects the paper 8 that travels along the conveyance path. Yes.

FIG. 4 shows an example of the arrangement of the remaining sheet detection sensor 6 in the fixing device 1. In this example, the optical axis of the emitted light from the remaining paper detection sensor 6 is directed to the surface of the heating roller 2 to detect direct winding. By arranging the sensor 6 above the conveyance path and directing the optical axis directly to the outer peripheral surface of the fixing roller, it is possible to detect the presence or absence of paper (= presence of winding).
However, as disclosed in Patent Document 1, the sensors are vulnerable to heat, and it is desirable that the sensors be located away from the heating roller 2 and below the conveyance surface. That is, with this configuration, there is a drawback that the remaining sheet detection sensor 6 is directly affected by the heat flow. For this reason, as shown in FIG. 4, when the remaining sheet detection sensor 6 is disposed above the conveyance surface, it is directly affected by the hot air flow, so that heat-proof measures and heat resistance are required, and the cost increases. End up.
Further, when the remaining sheet detection sensor (wrapping sensor) 6 is not provided, winding is determined when the sheet transport sensor 7 provided downstream of the fixing nip portion detects that the leading end of the sheet has not been reached. In this case, in most cases, a predetermined time has elapsed since the actual winding has occurred.
FIG. 5 is a schematic view showing another example of a fixing device having a detecting means for detecting a winding state other than the separation claw. 5, the configuration is almost the same as that in FIG. 4, and therefore the same members as those in FIG.
FIG. 5 shows an example in which the remaining sheet detection sensor 6 is provided downstream of the heating roller 2 and below the conveyance path. The remaining sheet detection sensor 6 is provided below the lower conveyance guide plate 10 and is arranged so that the optical axis of the emitted light faces the outer peripheral surface of the heating roller 2. Thereby, the presence of the sheet can be detected when the winding as shown by the broken line occurs.
JP-A-10-198216

In order to detect the winding jam at an early stage, it is desirable to directly detect the passage of the sheet on the surface of the heating roller 2 by the remaining sheet detection sensor 6 during the sheet conveyance process. However, when the remaining sheet detection sensor 6 is provided below the heating roller 2 in consideration of avoiding the influence of heat, the optical axis is blocked even when the sheet 8 is normally conveyed. The presence of the paper 8 is detected. Eventually, the presence / absence of winding of the paper is determined by the arrival state of the downstream paper transport sensor (not reached after a certain time), and deterioration of the winding state is inevitable.
In view of the above, the object of the present invention is to detect a wrapping jam as soon as possible and more reliably, thereby reducing the damage to the image forming apparatus to be applied and greatly improving the jam handling performance. It is an object of the present invention to provide a fixing device and an image forming apparatus including the fixing device.

In order to solve the above problems, the invention according to claim 1, a fixing roller pair composed of a pressure roller for heating roller and pressed against this for fixing the toner image transferred onto the paper, the A first optical sensor as a paper transport sensor for detecting that the paper is carried out from the pair of fixing rollers to a paper transport path, and a remaining paper for detecting whether the paper is wound around the heating roller A second optical sensor as a detection sensor, and a control for determining that the paper is wound around the heating roller when the second optical sensor detects the paper without the first optical sensor detecting the paper. and means, a second optical sensor, is respectively disposed between the downstream of the fixing roller pair in the sheet conveying direction, the first optical sensor, and the fixing roller pair and the second optical sensor And a first optical sensor and the second optical sensor, wherein when viewed from the sheet conveying path A on the side where there is a pressure roller, the paper is that the extension line of the outgoing light crosses from each of said sensors it is arranged to lie side where said heat roller viewed from the conveying path, wherein, when determining the wrapping around the said heating roller of the sheet is characterized by causing reversing the fixing roller pair.
According to a second aspect of the present invention, when the control unit determines that the sheet is not wrapped around the heating roller, the control unit moves the sheet to the downstream side of the fixing roller pair or to the outside of the apparatus. The fixing device according to claim 1 is discharged.
According to a third aspect of the present invention, there is provided an image forming apparatus including the fixing device according to the first or second aspect.

  According to the present invention, when the paper is wound around one of the fixing roller pair (usually a heating roller), the fixing device reverses the fixing roller driving means to eliminate the restriction at the front end of the paper. And the jam removability can be greatly improved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing a configuration of a fixing device to which the present invention is applied. In FIG. 1, a pair of fixing rollers constituting a fixing device 1 includes a heating roller 2 incorporating a heater 4, and a pressure roller 3 that presses the heating roller 2 at its outer peripheral surface to form a fixing nip portion, and downstream thereof. On the side, a separation claw 5 for separating the paper 8 conveyed to the fixing nip portion from the heating roller 2 is provided.
Further, on the downstream side of the fixing nip portion, a sheet conveyance sensor 7 for detecting the sheet 8 traveling on the conveyance path and a remaining sheet detection sensor 6 are sequentially arranged. The conveyance path of the paper 8 is formed by an upper conveyance guide 9 and a lower conveyance guide 10, and the sensors 7 and 6 are, for example, reflection type photosensors, both of which are arranged below the lower conveyance guide 10. Light emitted from the sensors 7 and 6 is configured to be able to individually detect paper passing through the transport path without being shielded, or paper wrapped around the peripheral surface of the heating roller 2.
That is, the sheet conveyance sensor 7 is provided between the remaining sheet detection sensor 6 and the fixing nip portion. Further, the optical axes of the remaining sheet detection sensor 6 and the sheet conveyance sensor 7 are arranged so as not to intersect in the conveyance path.
In addition, it is important that the emitted light from the remaining paper detection sensor 6 is directed to the outer periphery of the heating roller 2 and downstream of the separation claw 5, and the state where the leading end of the paper slips through the separation claw 5 and is wound around the heating roller Can be detected.
In this configuration, a control means (CPU) (not shown) determines that the paper 8 is in a normal state when the paper detection sensor 7 detects the paper 8 first, and the remaining paper detection sensor 6 detects the paper 8 first. If it is, it can be instantly determined that it is wound. When it is determined that the paper 8 is wound, the control unit immediately stops the driving of the fixing device 1.
If the paper detection sensor 7 is at the position 7 'indicated by the dotted line in the drawing and its optical axis intersects with the optical axis of the remaining paper detection sensor 6, which sensor detects the paper 8 first. Since it does not know whether to detect, the order with respect to determination occurs, and the determination condition becomes complicated. If the remaining sheet detection sensor 6 has detected first, the determination of the wrapping state is performed after waiting for the determination of the state of the sheet transport sensor 7.
Normally, detection of failure of the paper transport sensor 7 has a certain margin, so the timing for stopping it is delayed accordingly. Generally, if a target sensor does not detect within a predetermined time (the above margin), it is determined that the sensor has not been reached. Therefore, in the present invention, the non-delivery detection (non-reaching determination) of the paper transport sensor 7 is not used for the winding determination.

また、本発明を適用した定着装置１を備えた画像形成装置において、定着装置以外の箇所でジャムが発生する等、何らかの理由でやむを得ず加熱ローラ２（定着ローラ対２、３）を停止させなければならない場合が発生する。
このとき、定着装置１を通過中の用紙８が存在した場合に、この用紙８を用紙搬送センサ７が検知していれば、定着ローラニップ部に用紙８が残留している可能性が高い。
そこで、上記の巻き付き有無判定条件より、巻き付きが無いと判断した場合は、加熱ローラ２の駆動を再開して再搬送させて、定着ローラニップ部に残留している用紙８を下流側へ移動させる。
例えば、用紙８を用紙搬送センサ７のオフ（用紙後端抜け）まで退避させるか、もしくは定着装置１外へ退避させる。これにより、ジャム除去性及び安全性が大幅に向上する。これは本発明の重要な効果である。 FIG. 2 is a schematic view showing another fixing device to which the present invention is applied. 2, the configuration is almost the same as that of FIG. 1, and therefore, the same members as those of FIG.
The heating roller 2 is rotated clockwise by a drive motor 11 that is schematically shown to convey the paper 8 in the conveyance direction from the right side to the left side in the drawing. When the control means determines that the paper 8 is wound, the control means once stops (immediately cuts) the drive motor 11 and performs reverse rotation again.
At this time, the paper is reversely rotated until the front end of the paper is retracted and the front end of the separation claw 5 is surely removed. As a result, the front end of the paper is not restrained during the jam processing, and the jam removal property of the remaining paper is greatly improved. This is an important effect of the present invention. Conditions for determining the presence or absence of winding in each sensor state are shown below.

Further, in the image forming apparatus including the fixing device 1 to which the present invention is applied, the heating roller 2 (fixing roller pair 2 and 3) must be stopped for some reason, such as a jam occurring at a location other than the fixing device. There are cases where this is not possible.
At this time, if there is a sheet 8 passing through the fixing device 1, if the sheet conveyance sensor 7 detects the sheet 8, the possibility that the sheet 8 remains in the fixing roller nip portion is high.
Therefore, when it is determined that there is no winding based on the above-described winding presence / absence determination condition, the driving of the heating roller 2 is resumed and transported again, and the paper 8 remaining in the fixing roller nip portion is moved downstream.
For example, the paper 8 is withdrawn until the paper conveyance sensor 7 is turned off (out of the rear end of the paper) or withdrawn outside the fixing device 1. This greatly improves jam removal and safety. This is an important effect of the present invention.

FIG. 3 is a schematic view showing an image forming apparatus to which the fixing device according to the present invention is applied. In FIG. 3, a reading unit 12 is provided for scanning a document placed on a pressure plate. The reading unit 12 includes a contact glass 20 on which an original is placed and an optical scanning system.
The optical scanning system includes an exposure lamp 13, a first mirror 14, a second mirror 17, a third mirror 18, a lens 15, a CCD image sensor 16, and the like. The original image is read by the CCD image sensor 16 and converted into an electrical signal for processing.
In a sheet document automatic reading apparatus A for automatically reading a sheet document, a document (not shown) placed on a document table B is sent to the position of a document reading sensor G by a feed roller C. The original passes through the original reading sensor G at a constant speed, and at this time, the image on the front side of the original is read by the original reading sensor G.
The read image data is sequentially stored in an image memory (not shown) after image processing (various corrections, compression, etc.). The writing unit 49 includes a laser output unit 19, an imaging lens 21, and a mirror 22, and a laser beam output from the writing unit 49 is applied to the image forming type photoconductor 30.
The procedure for printing an image formed on the photoreceptor 30 is roughly as follows. The sheets stacked on the first tray 23, the second tray 24, and the third tray 25 are fed by the first paper feeding device 26, the second paper feeding device 27, and the third paper feeding device 28, respectively, and are vertically transported. 29 is conveyed to a position where it abuts against the photoreceptor 30.
The image data on the image memory is written onto the photoconductor 30 by the laser light from the writing unit 49, and a toner image is formed by passing through the developing unit 35.
The toner image on the photosensitive member 30 is transferred while the sheet is conveyed by the conveying belt 31 at the same speed as the rotation of the photosensitive member 30. Thereafter, the image is fixed by the fixing device 1 and is discharged to the paper discharge tray 33 by the paper discharge unit 32.

When images are to be formed on both sides, the reversing path switching claw (not shown) is switched for the paper fed from each of the paper feed trays 23 to 25 and imaged. As a result, the sheet is conveyed to the duplex entrance conveyance path 38 without being guided to the discharge tray 33 side, is guided to the reversing unit 37 provided in the duplex conveyance unit 36, and is temporarily stored in the switchback conveyance 41.
The paper is fed back in the reverse direction (re-feeding direction) by the reverse conveying means, guided downward by a reverse paper discharge switching claw (not shown), reversed, and sent to a double-sided intermediate conveyance path 43 provided below the reverse paper feeding switching claw.
Then, the intermediate conveying means 40 and the double-sided outlet conveying means 42 connected to a driving source (motor) (not shown) are again sent to the vertical conveying unit 29 to print an image on the back surface and then discharged.
When the paper is reversed and discharged, the paper that has been switched back by the reversing unit 37 is sent out to the reverse paper discharge conveyance path 39 by the paper discharge reverse switching claw without passing through the double-sided intermediate conveyance 43 and discharged again. It returns to the unit 32 and is discharged out of the main body.
The sheet discharged from the main body is discharged to either the discharge tray 33 or the finisher 44 of the main body by a discharge destination switching claw (not shown). The paper discharged to the finisher 44 passes through the punch unit 48 for punch hole processing, and is once stacked on the stack tray 45 for stapling. After all the sheets are collected in the stack tray, the sheet bundle is bound by the stapler unit 46 and discharged to the discharge tray 47.
When the operation of the present invention as described above, that is, when it is determined that the sheet is not wound around the fixing roller, the sheet remains on the fixing nip when the sheet is discharged downstream from the fixing nip or outside the apparatus. One of the retracting means is to send the sheet to the switchback transport 41 when the transported sheet is transported again to the outside of the fixing device (downstream side).

1 is a schematic diagram illustrating a fixing device to which the present invention is applied. FIG. 6 is a schematic diagram showing another fixing device to which the present invention is applied. 1 is a schematic diagram showing an image forming apparatus to which a fixing device according to the present invention is applied. Schematic which shows an example of the fixing device which has a detection means to detect a winding state other than a separation nail. Schematic which shows the other example of the fixing device which has a detection means to detect a winding state other than a separation nail.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixing device, 2 Fixing roller, 5 Separation claw, 6 Remaining paper detection sensor, 7 Paper transport sensor, 8 Paper, 9 Transport path (upper transport guide), 10 Transport path (lower transport guide), 11 Drive motor

Claims (3)

A pair of fixing rollers comprising a heating roller for fixing the toner image transferred on the paper and a pressure roller in pressure contact with the heating roller;
A first optical sensor as a paper transport sensor for detecting that the paper has been carried out from the pair of fixing rollers to a paper transport path ;
A second optical sensor as a remaining paper detection sensor for detecting whether the paper is wound around the heating roller;
Control means for determining that the paper is wound around the heating roller when the second optical sensor detects the paper without the first optical sensor detecting the paper;
The second optical sensor, downstream of said fixing roller pair in the sheet conveying direction, the first optical sensor is arranged between the fixing roller pair and the second optical sensor, and the first optical sensor and the second optical sensor, the a is viewed from the sheet conveying path side where said pressure roller, said heating roller that extension of the light emitted from each of said sensors intersect is viewed from the sheet transport path Are arranged to exist on the side
Wherein, when determining the wrapping around the said heating roller of the sheet fixing device characterized by causing reversing the fixing roller pair. 2. The control unit according to claim 1, wherein when it is determined that the sheet is not wound around the heating roller, the control unit discharges the sheet to the downstream side of the fixing roller pair or to the outside of the apparatus. Fixing device.   An image forming apparatus comprising the fixing device according to claim 1.

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